1. Field of the Invention
The present invention relates to an output adjustment method for a lens position sensor of an optical disk device for adjusting the output of the lens position sensor that detects a position of an object lens of the optical head, and the optical disk device, and more particularly to an output adjustment method for a lens position sensor of an optical disk device that detects a neutral point accurately even if the output of the lens position sensor changes due to the change with the passage time of the lens position sensor, and the optical disk device thereof.
2. Description of the Related Art
Because of advancements in optical storage technology, optical disk devices using optical storage disks are widely used for compact disk (CD) devices, DVD (Digital Versatile Disk) devices, magneto-optical (MO) disk drives and others.
As FIG. 21 shows, in such an optical disk device, light is irradiated from an optical head 2000 onto an optical disk 1000, and a reflected light thereof is received by an optical detector 2030 for reading. And the focus position shift FES of the irradiated light and the track position shift TES are also detected from the reflected light.
In other words, spiral or concentric tracks have been formed on the optical disk 1000, and it is effective for fine reading and writing to focus the irradiated light on the recording face of the disk and position the light to the track position of the disk.
For this, the focus control mechanism for controlling the focus of the objective lens 2010 of the optical head 2000, according to the detected focus position shift and the track control mechanism 2020 for controlling the objective lens 2010 to position the track position, according to the detected track position shift, are provided.
To control the lens position, the lens position sensor 2040 is installed on the lens 2010, and the signal LPOS, according to the displacement of the lens 2010, is acquired from the lens position sensor 2040, and the lens position is controlled based on the signal LPOS.
The lens position signal LPOS is used for locking so that the lens 2010 does not sway during seeking, and for removing the offset of the track position shift (error) signal.
As FIG. 23 shows, when the positional relationship of the optical head 2000 and the objective lens 2010 is not shifted, the relationship of the TES amplitude waveform and tracking position is expressed by a TES amplitude waveform having a symmetric sine wave of which center is the zero level (tracking position) indicated by the straight line. Since the center position of the TES waveform is exactly at the tracking position, a fine track servo can be implemented.
If the positional relationship between the optical head 2000 and lens 2010 shifts, however, offset is generated in the TES amplitude., and a shift occurs, as shown in FIG. 24. In the case of FIG. 24, the track servo is executed at the edge of the TES waveform, which makes the track servo unstable.
In this way, when the positional relationship of the optical head 2000 and lens 2010 shifts, this must be corrected, so the lens position is detected by the above mentioned lens position signal LPOS, and the offset of TES is corrected.
In this method of detecting the lens position, an error may be generated due to the change of the passage time and contamination of the sensor 2040, for example. In other words, as FIG. 22 shows, the lens shift amount and the output of the lens position sensor changes due to the change of the passage time, which makes it difficult to cancel the offset accurately.
To correct this change of output, a differential detection type has been proposed, where a pair of light receiving sections are provided to the lens position sensor 2040, so as to obtain the difference between the outputs of the pair of light receiving sections (e.g. Japanese Patent Application Laid-Open No. 7-235064).
A magneto-optical disk device, which is a type of optical disk device, is often used as a stationary type, so the position of the device rarely changes. However today magneto-optical disks are becoming compact, and are seen used in portable equipment fields. And if used as portable equipment, the attitude of the device when used is unknown.
If the attitude changes, the objective lens, which is supported such that moving in the track position is possible, tends to cause a position shift between the lens position and optical head, due to gravity and other influences, and the amount of shift tends to increase.
If the differential detection type in prior art is used for correcting this, a pair of detection sections and a differential circuit must be installed, so it is not preferable to decrease cost and size for portable equipment, since the number of components increases and mechanical components become complicated.
Also considering the change of the passage time, the characteristics of the initial status change because the light intensity of the LED section of the sensor changes, or the light receiving sensitivity of the sensor changes due to dust which attaches to the detector section, for example. Therefore, if a pair of light receiving sections is installed, they do not always deteriorate in the same way, even if the differential type is used, and correction of the change of output may be difficult in some cases.